Field of the Invention
For more than ten years, attempts to implant devices in human jaw bones where natural teeth are missing have not been successful to the point where even one moderately well accepted design exists. Experience to date has demonstrated that remodeling of the jaw bone to accommodate the nonphysiological stress patterns introduced by the artificial implant generally causes an undesired reduction in the total volume of bone. It is a principal of physiology that bone develops shape and density according to the manner in which load is imposed on it. A change of shape or density on account of a change of loading is called bone remodeling. Further, the loss of bone is generally in that part of the jaw where the implant emerges from the bone to support the artificial tooth, bridge or other dental appliance. This loss of bone is at least partly attributed to the reduced stress in that part of the bone where the implant emerges from the bone. This occurrence has been reported particularly in patients fitted with blade type implants.
Functional loads imparted to a natural tooth or an implant are principally compression and bending. There is little likelihood of any significant torsion load being present. Current practice in implanting dental anchorage devices favors non-loading of the implant for an initial period of 2 to 4 months during which time the bone supporting the implant recovers from the trauma of the implantation procedure. This has been conveniently accomplished by using a two or more part device, where the bone anchorage part is implanted wholely within the jaw bone and the gum tissue is closed over the implant for the initial time period. One surface of the implant is approximately flush with the alveolar ridge of the mandible or maxilla and through this surface there has been provided a female thread, into which a second part of the prosthesis having a threaded male stem can be fastened when the gum tissue is penetrated for so doing.
The above known implanted parts may be externally smooth or threaded posts or cylinders, or blades. Any of which may be of metal, carbon, plastic or ceramic, either solid or porous, and uncoated or coated with a variety of biologically acceptable materials.
To our knowledge all of the above are designed for approximately equal or uniform bony attachment to all imbedded surfaces, and certainly in no instance is there provision for enhanced bony fixation in the area near the alveolar ridge and for less enhanced bony attachment to that part of the implant which extends relatively more deeply into the jaw bone, either mandible or maxilla.
Accordingly, a primary object of the present invention is to provide a dental prosthesis for implantation in the jaw bone by which compression load to the prosthesis is transferred primarily to the bone area adjacent to the alveolar ridge in order to maintain and develop sound bone in this critical area by stress remodeling of the bone; while at the same time transferring to the bone, lateral compressive stress reactions to bending loads applied to the implant, (1) as lateral compressive stress at the area adjacent the alveolar ridge and, (2) as lateral compressive stress at an area displaced from the alveolar ridge wherein the above opposed lateral compressive stresses are within the physiological stress capacity of the jaw bone.
An additional object is to provide a dental implant where that part implanted within the jaw bone immediately adjacent the alveolar ridge has its external bone interface surface area increased by geometric features or surface texture and that part implanted distant from the alveolar ridge lacks features which would increase its surface area.
An additional object is to provide the part of a dental implant prostheseis which passes through the gum to be of high endurance strength by making this part to be without external surface discontinuities such as those created by the presently used screw threads.
An additional object is to provide a dental implant prosthesis which has immediate structural intimate relationship with the jaw bone in order to prevent motion between the prosthesis and the bone.
An additional object is to provide a system where the part of the dental implant which passes through the gum can be firmly anchored in any radial angular position. That is, security of fastening is not a function of rotary thread tightening or other limitation.
An additional object is to provide the above advantages while at the same time also providing a two part dental prosthesis which permits an initial implantation of only one part, which part lies flush within, or below, the alveolar ridge of the jaw bone, so that the gum may be closed for a time of healing of the bone, after which the second part which passes through the gum issue may be installed.